1. Field of the Invention
The present invention relates to a height adjuster for adjustment in height of a seat cushion of vehicle seat, and in particular to a structure of control portion of such seat height adjuster.
2. Description of Prior Art
Many of vehicle seats are each provided with a height adjuster (or what is otherwise described as “seat lifter”) of the type wherein operation of the associated control lever causes vertical movement of seat cushion of the seat to allow for adjustment in height of the seat.
For that purpose, the known height adjuster comprises: pivotal links operatively connected with the seat cushion; a drive shaft connected with one of those pivotal links; a brake unit (or lock unit) provided about the drive shaft to normally prevent rotation of the drive shaft itself, except as otherwise operated; and a control portion disposed at a point accessible by a seat occupant, such control portion including a control lever operatively connected with the afore-said drive shaft, so that the seat occupant can easily reach and operate the control lever.
Hence, operation of the control lever by the seat occupant actuates the brake unit to release the drive shaft from locked state and thus causes normal or reverse rotation of that drive shaft, thereby resulting in vertical movement of the pivot links, which in turn causes simultaneous vertical displacement of seat cushion. With such arrangement, the seat occupant can adjust his or her seating position to a desired level by operating the control lever.
In this kind of height adjuster, as disclosed for example from the Japanese Laid-Open Utility Model Publication No. 3-1838, the brake unit has a connecting shaft firmly connected with the drive shaft, the connecting shaft projecting outwardly from a seat cushion frame, and therefore, the control lever is disposed on the seat cushion frame at a point distant from the brake unit so as to avoid interference with that connecting shaft of brake unit. In this prior art, those control lever shaft and brake unit connecting shaft are respectively provided with two wheels in fixed way, and further, an endless belt or chain is extended and engaged between such two wheels, which constitutes a transmission means between the control lever and the drive shaft of height adjuster. Thus, rotation of the control lever is transmitted through such transmission means to both of the brake unit and drive shaft.
However, the foregoing height adjuster has been found defective in that the foregoing transmission means, or a whole of the endless belt, projects laterally from the outside of the seat cushion frame, thereby undesirably increasing a width of seat cushion. Moreover, in this height adjuster, a clearance is inevitably given between the endless belt and wheels, which causes an undesired play to rotation of the control lever, and also, the endless belt itself is elastic and extendible. As a result thereof, rattling and wobbling are easily caused in both of the control lever and endless belt and the efficiency of transmission becomes lower, as well.
In particular, the foregoing defective aspects must be avoided for a height adjuster that has the aforementioned brake unit, because the brake unit normally includes ratchet-type or clutch-type braking mechanism which requires stepwise fine operation of the control lever at quite short intervals to secure a step-by-step braking effect for precise adjustment in height of seat. Such required stepwise operation of the control lever can not be precisely transformed through the aforementioned transmission means to the drive shaft of the height adjuster.